[Toaster] [review-request] michaelw/toaster/fix-typeahead-behaviour

[Michael Wood]

This branch brings back the correct typeahead behaviour as a modular widget.

- New typeahead widget
- Switch to Implementation of widget in frontend
- Utility functions in the models so that the querysets which are used 
for the ToasterTables are the same queries that are used for the 
typeaheads.
- Added/Fixed typeahead widget unit tests

see also https://bugzilla.yoctoproject.org/show_bug.cgi?id=7152

* a465b19 bitbake: toastergui: tests Fix and more comprehensive 
typeahead unittest
* 4c71133 bitbake: toastergui: views Standardise the fields project 
layer response
* 592339b bitbake: toasterui: views Remove unused xhr_typeahead view 
definition
* dc7d764 bitbake: toastergui: libtoaster Throw an exception no url is 
specified
* 94c3f72 bitbake: toastergui: Switch to using the new toaster typeahead 
widget
* ead8702 bitbake: toastergui: Add typeaheads for layers, machines and 
recipes
* 09c6772 bitbake: toastergui: widgets Add a typeahead widget
* 9309429 bitbake: toastergui: tables Use util functions for the common 
querysets
* 0ba647b bitbake: toaster: orm Add util functions to return common 
querysets
* 691696f bitbake: toaster: orm Add util function to return the url to 
layerversion